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ZDZ Super 80 Mid-range

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Old 10-21-2008, 04:24 PM
  #1
lanpc
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Default ZDZ Super 80 Mid-range

I have a ZDZ Super 80 with header and canister muffler (From RC Showcase) and a 24x12 composite 3-blade propeller. I just changed out the Tennison carb with a Walbro carb, but I'm still having some mid-range issues. A group of us tried adjusting both the low speed and high speed needles, but could not smooth out the midrange. I've been told, by friends, that to either shorten the header, or shorten the exhaust tube (which is original and still kind of long) coming out the back of the canister muffler. But prior to doing any cutting, which we don't know would fix or cause more problems, I thought I would ask for HELP!.

Help!


Thanks,

Patrick

I got an email reply from Mike

With the TR-80, you MUST use the wraparound header at its full length. DO NOT SHORTEN IT.

We use this setup with the 26x12 2 blade and get 6400rpm.

The 24x12 should be close.

The silencer must be getting cooled sufficiently to work properly as well.

Please look at tell me what carb is installed on the engine.

I hope it is a Walbro WJ71.

Let me know.

Thanks,



Mike Dooley
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Old 10-23-2008, 11:27 AM
  #2
YBP
 
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Default RE: ZDZ Super 80 Mid-range

Hi.
Try adding a velocity stack to the carb if you don´t already have one.
It allows you to lean out the lowspeed needle more without the engine hesitating when opening the throttle from idle.
It has worked for me.

Lars.
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Old 10-23-2008, 12:58 PM
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arobatx
 
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Default RE: ZDZ Super 80 Mid-range

I've noticed the same thing....and like the funnels.

I have the WJ71 on my 80RV, 3w Carb funnel, and properly baffled cowl to direct airflow through the fins and out the bottom of the cowl... I then had no need to run a tube from the reference pressure fitting on the carb plate to a static box, or similar to correct for pressure changes at different throttle and/or attitude changes.
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Old 02-17-2009, 07:59 PM
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RAMMJETT
 
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Default RE: ZDZ Super 80 Mid-range

try to drop the pop off pressure on the regulator in the carb/this gives better transition from low to high speed /as the fuel is easier to draw from the main jet(their will be less lag or transition) main jet only opens at a given pressure & and these carbs are designed for idle & high speed primarly.a lighter spring can be obtained from most small motor shops .use of a small pressure pump & gauge can measure present spring pressure(pop off point)(mesure by putting pressure on the fuel line untill the regulator pops open). drop it by 25%. /a venturi can also help ,as it increases volicity of incoming air causing main jet to open more rapid .you will have a smooth & seamless curve . hope this helps Roger
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